For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (MEA) which includes a solid polymer electrolyte membrane, an anode provided on one side of the solid polymer electrolyte membrane, and a cathode provided on the other side of the solid polymer electrolyte membrane. The solid electrolyte membrane is a polymer ion exchange membrane. The membrane electrode assembly is sandwiched between separators to form a power generation cell (unit cell). Generally, several tens to hundreds of power generation cells are stacked together to form a fuel cell stack, e.g., for use in a vehicle.
In the fuel cell, as separators, metal separators of thin corrugated plates may be adopted. A wavy fuel gas flow field including a plurality of flow grooves is formed in a surface of the metal separator facing an anode, for allowing the fuel gas to flow along an electrode surface of the anode in a wavy pattern. A wavy oxygen-containing gas flow field including a plurality of flow grooves is formed in a surface of the metal separator facing a cathode, for allowing the oxygen-containing gas to flow along an electrode surface of the cathode in a wavy pattern.
As a fuel cell of this type, for example, a fuel cell stack disclosed in Japanese Laid-Open Patent Publication No. 2009-301996 is known. In this fuel cell stack, first power generation units and second power generation units are stacked together alternately, and a coolant flow field is formed in each space between the adjacent first and second power generation units. In each power generation unit, an electrolyte electrode assembly is formed by interposing an electrolyte between an anode and a cathode, and the electrolyte electrode assembly is sandwiched between metal separators. Further, in the metal separators, a wavy fuel gas flow field for supplying a fuel gas to the anode and a wavy oxygen-containing gas flow field for supplying an oxygen-containing gas to the cathode are provided.
In the first power generation unit, wavy flow grooves of the fuel gas flow field and wavy flow grooves of the oxygen-containing gas flow field are in the same phase. In the second power generation unit, wavy flow grooves of the fuel gas flow field and wavy flow grooves the oxygen-containing gas flow field are in the same phase, and are in different phases from the wavy flow grooves of the fuel gas flow field and the wavy flow grooves of the oxygen-containing gas flow field of the first power generation unit.
Further, in a fuel cell disclosed in Japanese Patent No. 3,599,280, a wavy fuel gas flow field including a plurality of flow grooves is formed in a surface of the metal separator facing an anode, for allowing the fuel gas to flow along an electrode surface of the anode in a wavy pattern, and a wavy oxygen-containing gas flow field including a plurality of flow grooves is formed in a surface of the metal separator facing a cathode, for allowing the oxygen-containing gas to flow along an electrode surface of the cathode in a wavy pattern.
The phase of the wavy reactant gas flow field (fuel gas flow field) of one of the adjacent fuel cells and the phase of the wavy reactant gas flow field (oxygen-containing gas flow field) of the other of the adjacent fuel cells are different. Therefore, the back surface of the wavy reactant gas flow field of the metal separator of one of the adjacent fuel cells and the back surface of the wavy reactant gas flow field of the metal separator of the other of the adjacent fuel cells are stacked together to form a coolant flow field between these back surfaces.